Tampa has better riding...

The Orlando are is a little lean on trails. Little/Big Econ State Forest (Snow Hill Road) is really the closest and even that is an hour+ from the attractions area (I assume that is where you will be). Your best bets will be Alafia, Santos, Wilderness Park, Boyette. As mentioned check out www.swampclub.org. Also www.omba.org. According to previous similar posts these shops rent bikes http://ajsbikesandboards.com/site/intro.cfm and www.cbebikes.com. Good luck!